Fix use-package :custom-face to set face-defface-spec (bug#77928)

By default, `face-set-spec' sets the override face spec, so face
attributes are combined with defaults rather than replacing them.
This was a behavior change that was an apparently unintended
consequence of commit 6b344a9.

Also set the `face-modified' property, which causes Customize to
flag the face as changed outside Customize.

* doc/misc/use-package.texi (Faces): Document the behavior.
* lisp/use-package/use-package-core.el (use-package-handler/:custom-face):
(use-package): Improve docstring to reflect implementation.
* test/lisp/use-package/use-package-tests.el
(use-package-test/:custom-face-1): (use-package-test/:custom-face-2):
(use-package-test/:custom-face-3): (use-package-test/:custom-face-4):
Add tests.

1 files changed, 34 insertions, 6 deletions

diff --git a/test/lisp/use-package/use-package-tests.el b/test/lisp/use-package/use-package-tests.el
index 8554b37d5b8..b221c5de5c1 100644
--- a/test/lisp/use-package/use-package-tests.el
+++ b/test/lisp/use-package/use-package-tests.el
@@ -1153,7 +1153,12 @@
   (match-expansion
    (use-package foo :custom-face (foo ((t (:background "#e4edfc")))))
    `(progn
-      (apply #'face-spec-set (backquote (foo ((t (:background "#e4edfc"))))))
+      (progn
+        (apply #'face-spec-set
+               (append (backquote (foo ((t (:background "#e4edfc")))))
+                       '(face-defface-spec))
+               )
+        (put 'foo 'face-modified t))
       (require 'foo nil nil))))
 
 (ert-deftest use-package-test/:custom-face-2 ()
@@ -1163,19 +1168,42 @@
      (example-1-face ((t (:foreground "LightPink"))))
      (example-2-face ((t (:foreground "LightGreen")))))
    `(progn
-      (apply #'face-spec-set
-             (backquote (example-1-face ((t (:foreground "LightPink"))))))
-      (apply #'face-spec-set
-             (backquote (example-2-face ((t (:foreground "LightGreen"))))))
+      (progn
+        (apply #'face-spec-set
+               (append (backquote (example-1-face ((t (:foreground "LightPink")))))
+                       '(face-defface-spec)))
+        (put 'example-1-face 'face-modified t))
+      (progn
+        (apply #'face-spec-set
+               (append (backquote (example-2-face ((t (:foreground "LightGreen")))))
+                       '(face-defface-spec)))
+        (put 'example-2-face 'face-modified t))
       (require 'example nil nil))))
 
 (ert-deftest use-package-test/:custom-face-3 ()
   (match-expansion
    (use-package foo :custom-face (foo ((t (:background "#e4edfc"))) face-defspec-spec))
    `(progn
-      (apply #'face-spec-set (backquote (foo ((t (:background "#e4edfc"))) face-defspec-spec)))
+      (progn
+        (apply #'face-spec-set
+               (append (backquote (foo ((t (:background "#e4edfc"))) face-defspec-spec))
+                       '(face-defface-spec)))
+        (put 'foo 'face-modified t))
       (require 'foo nil nil))))
 
+(ert-deftest use-package-test/:custom-face-4 ()
+  (defface use-package-test/base-face '((t (:background "green"))) "")
+  (defface use-package-test/face '((t (:inherit use-package-test/base-face))) "")
+  (use-package emacs
+    :custom-face
+    (use-package-test/face ((t (:foreground "blue")))))
+  (should (equal (face-foreground 'use-package-test/face nil t)
+                 "blue"))
+  (should (equal (face-background 'use-package-test/face nil t)
+                 nil))
+  (should (equal (get 'use-package-test/face 'face-modified)
+                 t)))
+
 (ert-deftest use-package-test/:init-1 ()
   (match-expansion
    (use-package foo :init (init))